This invention is generally in the field of methods for the treatment and prevention of inflammatory responses involving binding reactions with selections including GMP-140, ELAM-1, and lymphocyte-homing receptor.
The adherence of platelets and leukocytes to vascular surfaces is a critical component of the inflammatory response, and is part of a complex series of reactions involving the simultaneous and interrelated activation of the complement, coagulation, and immune systems.
The complement proteins collectively play a leading role in the immune system, both in the identification and in the removal of foreign substances and immune complexes, as reviewed by Muller-Eberhard, H. J., Ann. Rev. Biochem. 57:321-347 (1988). Central to the complement system are the C3 and C4 proteins, which when activated covalently attach to nearby targets, marking them for clearance. In order to help control this process, a remarkable family of soluble and membrane-bound regulatory proteins has evolved, each of which interacts with activated C3 and/or C4 derivatives. The coagulation and inflammatory pathways are regulated in a coordinate fashion in response to tissue damage. For example, in addition to becoming adhesive for leukocytes, activated endothelial cells express tissue factor on the cell surface and decrease their surface expression of thrombomodulin, leading to a net facilitation of coagulation reactions on the cell surface. In some cases, a single receptor can be involved in both inflammatory and coagulation processes.
Leukocyte adherence to vascular endothelium is a key initial step in migration of leukocytes to tissues in response to microbial invasion. Although a class of inducible leukocyte receptors, the CD11-CD18 molecules, are thought to have some role in adherence to endothelium, mechanisms of equal or even greater importance for leukocyte adherence appear to be due to inducible changes in the endothelium itself.
Activated platelets have also been shown to interact with both neutrophils and monocytes in vitro. The interaction of platelets with monocytes may be mediated in part by the binding of thrombospondin to platelets and monocytes, although other mechanisms have not been excluded. The mechanisms for the binding of neutrophils to activated platelets are not well understood, except that it is known that divalent cations are required. In response to vascular injury, platelets are known to adhere to subendothelial surfaces, become activated, and support coagulation. Platelets and other cells may also play an important role in the recruitment of leukocytes into the wound in order to contain microbial invasion.
Endothelium exposed to "rapid" activators such as thrombin and histamine becomes adhesive for neutrophils within two to ten minutes, while endothelium exposed to cytokines such as tumor necrosis factor and interleukin-1 becomes adhesive after one to six hours. The rapid endothelial-dependent leukocyte adhesion has been associated with expression of the lipid mediator platelet activating factor (PAF) on the cell surface, and presumably, the appearance of other endothelial and leukocyte surface receptors. The slower cytokine-inducible endothelial adhesion for leukocytes is mediated, at least in part, by an endothelial cell receptor, ELAM-1, that is synthesized by endothelial cells after exposure to cytokines and then transported to the cell surface, where it binds neutrophils. The isolation, characterization and cloning of ELAM-1 is reviewed by Bevilacqua, et al., in Science 243, 1160-1165 (1989). A peripheral lymph node homing receptor, also called "the murine Mel 14 antigen", "Leu 8", the "Leu 8 antigen" and "LAM-1", is another structure on neutrophils, monocytes, and lymphocytes that binds lymphocytes to high endothelial venules in peripheral lymph nodes. The characterization and cloning of this protein is reviewed by Lasky, et al., Cell 56, 1045-1055 (1989) (mouse) and Tedder, et al., J. Exp. Med. 170, 123-133 (1989).
GMP-140 (granule membrane protein 140), also known as PADGEM, is a cysteine-rich and heavily glycosylated integral membrane glycoprotein with an apparent molecular weight of 140,000 as assessed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). GMP-140 was first purified from human platelets by McEver and Martin, J. Biol. Chem. 259:9799-9804 (1984). The protein is present in alpha granules of resting platelets but is rapidly redistributed to the plasma membrane following platelet activation, as reported by Stenberg, et al., (1985). The presence of GMP-140 in endothelial cells and its biosynthesis by these cells was reported by McEver, et al., Blood 70(5) Suppl. 1:355a, Abstract No. 1274 (1987). In endothelial cells, GMP-140 is found in storage granules known as the Weibel-Palade bodies. GMP-140 (called PADGEM) has also been reported to mediate the interaction of activated platelets with neutrophils and monocytes by Larsen, et al., in Cell 59, 305-312 (October 1989) and Hamburger and McEver, Blood 75:550-554 (1990).
The cDNA-derived amino acid sequence, reported by Johnston, et al., in Cell 56, 1033-1044 (Mar. 24, 1989), and in U.S. Ser. No. 07/320,408 filed Mar. 8, 1989, indicates that it contains a number of modular domains that are likely to fold independently. Beginning at the N-terminus, these include a "lectin" domain, an "EGF" domain, nine tandem consensus repeats similar to those in complement binding proteins, a transmembrane domain (except in a soluble form that appears to result from differential splicing), and a cytoplasmic tail.
When platelets or endothelial cells are activated by mediators such as thrombin, the membranes of the storage granules fuse with the plasma membrane, the soluble contents of the granules are released to the external environment, and membrane bound GMP-140 is presented within seconds on the cell surface. The rapid redistribution of GMP-140 to the surface of platelets and endothelial cells as a result of activation suggests that this glycoprotein could play an important role at sites of inflammation or vascular disruption.
ELAM-1, the homing receptor, and GMP-140 have been termed "selectins", based on their related structure and function.
The in vivo significance of platelet-leukocyte interactions has not been studied carefully. However, in response to vascular injury, platelets are known to adhere to subendothelial surfaces, become activated, and support coagulation. Platelets and other cells may also play an important role in the recruitment of leukocytes into the wound in order to contain microbial invasion. Conversely, leukocytes may recruit platelets into tissues at sites of inflammation, as reported by Issekutz, et al., Lab. Invest. 49:716 (1983).
The coagulation and inflammatory pathways are regulated in a coordinate fashion in response to tissue damage. For example, in addition to becoming adhesive for leukocytes, activated endothelial cells express tissue factor on the cell surface and decrease their surface expression of thrombomodulin, leading to a net facilitation of coagulation reactions on the cell surface. In some cases, a single receptor can be involved in both inflammatory and coagulation processes.
Proteins involved in the hemostatic and inflammatory pathways are of interest for diagnostic purposes and treatment of human disorders. However, there are many problems using proteins therapeutically. Proteins are usually expensive to produce in quantities sufficient for administration to a patient. Moreover, there can be a reaction against the protein after it has been administered more than once to the patient. It is therefore desirable to develop peptides having the same, or better, activity as the protein, which are inexpensive to synthesize, reproducible and relatively innocuous.
It is therefore an object of the present invention to provide peptides having activity of selectins, including GMP-140, ELAM-1, and lymphocyte homing receptor.
It is another object of the present invention to provide methods for using these peptides to inhibit leukocyte adhesion to endothelium or to platelets.
It is a further object of the present invention to provide methods for using these peptides to modulate the immune response and the hemostatic pathway.
It is yet another object of the present invention to provide peptides for use in diagnostic assays relating to GMP-140, ELAM-1, and lymphocyte homing receptor.
It is yet another object of the present invention to provide carbohydrate-based reagents, based on the structure of the leukocyte ligand for GMP-140, to inhibit GMP-140 - mediated adhesive interactions.